The experiment was conducted to examine the effect of various water stress levels on two varieties (V1: Swat 1, V2: Swat) of onion crop (Allium cepa. L) during the Rabi season 2015, and used RCBD with split plot arrangements of three replicates on clay loam soil. The stress levels comprised of full irrigation (Io), 90% of full irrigation (I1), 80% of full irrigation (I2) and 70% of full irrigation (I3). The soil moisture was determined by using FDR. Based on statistical results, the number of leaves (9.06) of both varieties at I0 was more as compared to the given stress conditions. The plant height was significantly influenced by the irrigation levels. Moreover, the data reflected that plant height was maximum (65.7 cm) at Io, while under the stress condition (I3), the plant height was minimum (48.7 cm). The maximum leaf length was observed at I0 (full irrigation) whereas, minimum value was obtained in I3 (28.82 cm). It was observed from the mean data that the maximum leaf width was 1.1 cm, 1.077 cm, 0.928 cm, and 0.796 cm at I0, I1, I2 and I3 respectively. Bulb diameter of onion crop was significantly influenced by the irrigation levels however; the effect on varieties and the interaction between varieties and irrigation were non-significant. Percent Rotten Bulb in each treatment was not significantly influenced by the irrigation levels. Hence, both varieties showed same average values of the percent rotten bulb (9% each). Number of roots per plant showed less difference among all the treatments. It was clear from the data that the root length was highly affected by the irrigation levels. The minimum root length (21.9 cm) was observed at the application of I1 while the maximum root length (29.15 cm) was noticed at I3. The maximum bulb yield of onion crop (2.85 tons ha-1) was obtained when treated with I0. Therefore, it is concluded that both varieties showed negative response to extreme deficit irrigation levels below 90% while higher irrigation stress levels gave positive response in terms of yield and water use efficiency